1. Field of the Invention
This disclosure relates to the field of semiconductor memory devices, and more particularly, to an output driver of a semiconductor memory device.
2. Description of the Related Art
When a semiconductor memory device is used in a system, load on an output terminal, i.e., an output pad, of the semiconductor memory device is large. Thus, a semiconductor memory device includes an output driver for driving an output pad. In a synchronous system, the slew rate of a signal output from an output driver has a close relationship to signal integrity, such as causing the switching noise of a system. In general, as the operating frequency increases, signal integrity decreases. Thus, the slew rate of an output signal of an output driver should be controlled based on a frequency resulting in the lowest signal integrity when a memory system that operates in a wide frequency range is designed.
However, in conventional output drivers, the correlation between operating frequency and slew rate is not considered. The driving capability of the conventional output driver is preset by the sizes of a pull-up transistor and a pull-down transistor. Accordingly, the conventional output driver cannot effectively control the slew rate of the output signal according to a variation in the operating frequency.
Embodiments of the invention address these and other disadvantages of the conventional art.